The present invention relates to a hose rupture control valve unit (hose rupture valve), which is provided in a hydraulic machine, such as a hydraulic excavator, for preventing a drop of a load upon rupture of a cylinder hose.
In a hydraulic machine, e.g., a hydraulic excavator, there is a need for preventing a drop of a load even if a hose or steel pipe for supplying a hydraulic fluid to a hydraulic cylinder, serving as an actuator for driving the load, e.g., an arm, should be ruptured. To meet such a need, a hose rupture control valve unit, also called a hose rupture valve, is provided in the hydraulic machine. FIG. 14 is a hydraulic circuit diagram showing a typical conventional hose rupture control valve unit, and FIG. 15 is a sectional view of the hose rupture control valve unit.
Referring to FIGS. 14 and 15, a hose rupture control valve unit 200 comprises a housing 204 provided with two input/output ports 201, 202 and a reservoir port 203. The input/output port 201 is directly attached to a bottom port of a hydraulic cylinder 102, the input/output port 202 is connected to one of actuator ports of a control valve 103 via a hydraulic hose 105, and the reservoir port 203 is connected to a reservoir 109 via a drain hose 205. Within the housing 204, there are provided a main spool 211 operated with a pilot pressure supplied as an external signal from a manual pilot valve 108, a check valve 212 for fluid supply, a poppet valve body 214 controlled by a pilot portion 213 which is provided on the main spool 211, and an overload relief valve 215 for releasing an abnormal pressure.
In the conventional hose rupture control valve unit 200 having the above-described construction, a hydraulic fluid is supplied to the bottom side of the hydraulic cylinder 102 by supplying the hydraulic fluid from the control valve 103 to the bottom side through the fluid-supply check valve 212 in the valve unit 200. Also, the hydraulic fluid is discharged from the bottom side of the hydraulic cylinder 102 by operating the main spool 211 of the valve unit 200 with the pilot pressure, as an external signal, so as to first open the poppet valve body 214 controlled by the pilot portion 213 which is provided on the main spool 211, and to then open a variable throttle portion 211a also provided on the main spool 211, thereby draining the hydraulic fluid to the reservoir 109 while controlling a flow rate of the hydraulic fluid.
The poppet valve body 214 is provided in series with the main spool 211, and has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder 102.
The overload relief valve 215 functions to drain the hydraulic fluid and prevent hose rupture in case that an excessive external force acts upon the hydraulic cylinder 102 and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder 102 is brought into a high-pressure level.
Also, if the hydraulic hose 105 leading from the control valve 103 to the input/output port 202 should be ruptured, the check valve 212 and the poppet valve body 214 are closed to prevent a drop of a load supported by the hydraulic cylinder 102. In such an event, by operating the main spool 211 with the pilot pressure from the manual pilot valve 108 and adjusting an opening area of the variable throttle portion 211a, it is possible to slowly contract the hydraulic cylinder 102 under action of the weight of the load itself and to move the load to a safety position.
Numerals 107a and 107b denote main relief valves for limiting a maximum pressure in the circuit.
Further, JP, A 3-249411 discloses a hose rupture control valve unit utilizing a proportional seat valve to reduce an overall size of the valve unit. FIG. 16 shows the disclosed hose rupture control unit.
Referring to FIG. 16, a hose rupture control valve unit 300 comprises a housing 323 provided with an input port 320, a work port 321 and a reservoir port 322. The input port 320 is connected to one of actuator ports of a control valve 103, the work port 321 is connected to a bottom port of a hydraulic cylinder 102, and the reservoir port 322 is connected to a reservoir 109 via a drain hose 205. Within the housing 323, there are provided a check valve 324 for fluid supply, a proportional seat valve 325, an overload relief valve 326, and a pilot valve 340. The pilot valve 340 is operated with a pilot pressure supplied as an external signal from a manual pilot valve 108 (see FIG. 14), and the proportional seat valve 325 is operated with the operation of the pilot valve 340. The overload relief valve 326 is incorporated in the proportional seat valve 325.
A hydraulic fluid to the bottom side of the hydraulic cylinder 102 is supplied by supplying the hydraulic fluid from the control valve 103 to the bottom side through the fluid-supply check valve 324 in the valve unit 300. Also, the hydraulic fluid is discharged from the bottom side of the hydraulic cylinder 102 by operating the pilot valve 340 of the valve unit 300 with the pilot pressure, as an external signal, to open the proportional seat valve 325, thereby draining the hydraulic fluid to the reservoir 109 while controlling a flow rate of the hydraulic fluid. The proportional seat valve 325 has the function (load check function) of reducing the amount of leakage in a condition of holding the load pressure on the bottom side of the hydraulic cylinder 102.
The overload relief valve 326 functions to open the proportional seat valve 325 for draining the hydraulic fluid and preventing hose rupture in case that an excessive external force acts on the hydraulic cylinder 102 and the hydraulic pressure supplied to the bottom side of the hydraulic cylinder 102 is brought into a high-pressure level.
Also, if a hydraulic hose 105 leading from the control valve 103 to the input port 320 should be ruptured, the check valve 324 and the proportional seat valve 325 are closed to prevent a drop of a load supported by the hydraulic cylinder 102. In such an event, by operating a spool 341 of the pilot valve 340 with the pilot pressure and adjusting an opening area of the proportional seat valve 325, it is possible to slowly contract the hydraulic cylinder 102 under action of the weight of the load itself and to move the load to a safety position.
However, the above-described prior arts have a problem that it is difficult to reduce a pressure loss and to cut down an overall size and production cost of the valve unit.
More specifically, in the prior art shown in FIGS. 14 and 15, various components, i.e., the check valve 212 for fluid supply, the main spool 211, the poppet valve body 214 controlled by the pilot portion 213 provided on the main spool 211, and the overload relief valve 215, are separately provided corresponding to the respective functions. Therefore, incorporating all those components in the housing 204 of a certain restricted size imposes a limitation on sizes of the individual components. Also, there has been a difficulty in reducing the production cost.
On the other hand, since all of the hydraulic fluid discharged from the hydraulic cylinder 102 passes through the main spool 211, a spool valve body of the main spool 211 is required to have a larger diameter. Further, because of the main spool 211 and the poppet valve body 214 being provided in series, the hydraulic fluid passes through these two valve elements at a large flow rate. Accordingly, when those parts are incorporated in the housing 204 of the certain restricted size, their sizes are necessarily limited, which may result in that a sufficient flow passage is not ensured and a pressure loss is increased. In addition, a pressure loss is also inevitably produced with such a construction that the hydraulic fluid passes at a large flow rate through both of the main spool 211 and the poppet valve body 214 provided in series.
The hose rupture control valve unit is mounted on the bottom side of a boom cylinder or the rod side of an arm cylinder. A boom and an arm, to which the boom cylinder and the arm cylinder are attached, are each a working member operated to rotate in the vertical direction. If the size of the housing 204 is selected to a relatively large value in consideration of the problem of a pressure loss, this selection would increase a risk that the hose rupture control valve unit may be damaged upon hitting against rocks or any other obstacles during the operation of the boom or the arm. It has been thus difficult to design the hose rupture control valve unit appropriately.
In the prior art disclosed in JP, A 3-249411, shown in FIG. 16, the overload relief valve 326 is incorporated in the proportional seat valve 325, which is controlled by the pilot valve 340, so that the proportional seat valve 325 has not only the function of the main spool 211, but also the functions of the poppet valve body 214 and the overload relief valve 215 in the above-described former prior art. Therefore, the number of components is reduced as compared with that needed in the above-described former prior art, and a reduction in size of the valve unit can be achieved to some extent while lessening a pressure loss. With this disclosed prior art, however, the check valve 324 for fluid supply is still an essential component. In other words, there is a demand for a further improvement in reducing the size and the production cost of the valve unit.
To overcome the problems mentioned above, the applicant proposed the following invention in JP, A 10-110776 (filing data: Apr. 21, 1998; corresponding to U.S. Appl. No. 09/294,431, EP Appl. No. 99201251.8, Korean Appl. No. 1999-13956, and Chinese Appl. No. 99105093.2).
xe2x80x9cA hose rupture control valve unit provided between a supply/drain port of a hydraulic cylinder and a hydraulic hose for controlling a flow rate of a hydraulic fluid coming out from the supply/drain port to the hydraulic hose in accordance with an external signal, wherein the valve unit comprises a poppet valve body serving as a main valve slidably disposed in a housing provided with a cylinder connecting chamber connected to the supply/drain port, a hose connecting chamber connected to the hydraulic hose, and a back pressure chamber, the poppet valve body being able to selectively cut off and establish communication between the cylinder connecting chamber and the hose connecting chamber, and changing an opening area depending on the shift amount thereof, and a spool valve body serving as a pilot valve disposed in a pilot passage connecting the back pressure chamber and the hose connecting chamber, and operated in accordance with the external signal to cut off and control a rate of pilot flow passing through the pilot passage depending on the shift amount thereof, the poppet valve body being provided with a feedback variable throttle passage which has an initial opening area when the poppet valve body is in a cutoff position, and increases an opening area thereof depending on the shift amount of the poppet valve body, thereby controlling the rate of pilot flow coming out from the cylinder connecting chamber to the back pressurexe2x80x9d.
With the thus-constructed valve unit of the earlier filed invention, in operation of supplying the hydraulic fluid to the bottom side of the hydraulic cylinder, since the feedback variable throttle passage has the initial opening area, the poppet valve body is opened when a pressure in the hose connecting chamber rises to a level higher than a load pressure, allowing the hydraulic fluid to be supplied to the bottom side of the hydraulic cylinder (conventional check valve function on the supply side).
In operation of discharging the hydraulic fluid from the bottom side of the hydraulic cylinder, when the spool valve body is operated in accordance with the external signal and the pilot flow is produced at a rate depending on the shift amount of the spool valve body, the poppet valve body is opened and the shift amount thereof is controlled depending on the pilot flow rate. Therefore, most of the hydraulic fluid on the bottom side of the hydraulic cylinder passes through the poppet valve body, whereas the remaining hydraulic fluid passes through the feedback variable throttle passage, the back pressure chamber and the spool valve body. Both the flows of the hydraulic fluid are then drained to the reservoir (conventional main spool function).
Further, in operation of holding the load pressure on the bottom side of the hydraulic cylinder, the poppet valve body is in the cutoff position and holds the load pressure, thereby reducing the amount of leakage (load check function).
Thus, the valve unit of the earlier filed invention can fulfill the least necessary functions of a hose rupture control valve unit (i.e., the check valve function on the supply side, the main spool function, and the load check function). Also, in the valve unit of the earlier filed invention, the poppet valve body is only one component arranged in a flow passage through which the hydraulic fluid passes at a large flow rate. It is hence possible to reduce a pressure loss, and to cut down an overall size and production cost of the valve unit.
An object of the present invention is to improve the earlier filed invention and to provide a hose rupture control valve unit which can reduce a pressure loss and cut down an overall size and production cost of the valve unit while ensuring various functions that are the least necessary as a hose rupture control valve unit, and which can offer smooth flow control characteristics and set a more variety of flow control characteristics.
(1) To achieve the above object, the present invention provides a hose rupture control valve unit provided between a supply/drain port of a hydraulic cylinder and a hydraulic hose for controlling a flow rate of a hydraulic fluid coming out from the supply/drain port to the hydraulic hose in accordance with an external signal, wherein the valve unit comprises a poppet valve body serving as a main valve slidably disposed in a housing provided with a cylinder connecting chamber connected to the supply/drain port, a hose connecting chamber connected to the hydraulic hose, and a back pressure chamber, the poppet valve body being able to selectively cut off and establish communication between the cylinder connecting chamber and the hose connecting chamber, and changing an opening area depending on the shift amount thereof; a feedback variable throttle passage provided in the poppet valve body, having an initial opening area when the poppet valve body is in a cutoff position, and increasing an opening area thereof depending on the shift amount of the poppet valve body; a first variable throttle portion disposed in a pilot passage connecting the back pressure chamber and the hose connecting chamber, and operated in accordance with the external signal to cut off and control a rate of pilot flow flowing from the cylinder connecting chamber to the hose connecting chamber through the feedback variable throttle passage, the back pressure chamber and the pilot passage; and a second variable throttle portion disposed in a sub-passage connecting the cylinder connecting chamber and the hose connecting chamber, and operated in accordance with the external signal to cut off and control a rate of sub-flow passing through the sub-passage.
The construction that the poppet valve body and the first variable throttle portion are provided and the poppet valve body includes the feedback variable throttle passage having an initial opening area, is the same as that of the earlier filed invention. With this construction, a pressure loss can be reduced and an overall size and production cost of the valve unit can be cut down, while ensuring various functions that are the least necessary as a hose rupture control valve unit.
Further, the second variable throttle portion is provided in the sub-passage so that it is given with the function of flow rate control in the fine operating range. Therefore, flow rate control in the fine operation range performed by the second variable throttle portion and control of the poppet valve body performed by the first variable throttle portion can made separately from each other. As a result, smooth flow control characteristics are obtained and a more variety of flow control characteristics can be set.
(2) In the above (1), preferably, opening timings of the first and second variable throttle portions are set such that the second variable throttle portion is opened earlier than the first variable throttle portion in accordance with the external signal.
With this feature, as mentioned in the above (1), the second variable throttle portion is given with the function of flow rate control in the fine operating range, and flow rate control in the fine operation range performed by the second variable throttle portion and control of the poppet valve body performed by the first variable throttle portion can made separately from each other.
(3) In the above (1), preferably, the first variable throttle portion and the second variable throttle portion are provided on separate spool valve bodies.
With this feature, the opening timings of the first variable throttle portion and the second variable throttle portion can be changed by not only the notch position of each of variable throttle portion, but also the strength of a spring acting upon each spool valve body. Therefore, flow control characteristics can be set with good accuracy.
(4) In the above (1), preferably, the first variable throttle portion and the second variable throttle portion are provided on the same spool valve body.
With this feature, the number of parts of the valve unit is reduced and the size of the valve unit can be further reduced.
(5) In any of the above (1) to (4), preferably, the hose rupture control valve unit further comprises means for cutting off the sub-passage after opening the poppet valve.
In the construction wherein the sub-passage and the second variable throttle portion are provided in addition to the pilot passage and the first variable throttle portion as set forth in the above (1), the pilot flow rate and the sub-flow rate join with each other on the side of the hose connecting chamber. Therefore, the flow rate increases in a joining area and the downstream side thereof, which increases a passage pressure loss and causes a jet stream in the joining area to such an extent that the pressure in the back pressure chamber is increased or fluctuated. This results in a possibility that the poppet valve body may not be opened to have an opening area as per instructed by an external signal and control of a main flow rate may be adversely affected.
By cutting off the sub-passage after opening of the poppet valve body, only the pilot flow passes through the joining area after the sub-passage has been cut off. It is therefore possible to suppress an increase of the passage pressure loss and the occurrence of a jet stream due to joining of the pilot flow rate and the sub-flow rate, and to reduce an influence upon the control of the main flow rate.
(6) In the above (5), preferably, the means for cutting off the sub-passage is a land portion provided on a spool valve body including the second variable throttle portion, the land portion cutting off a flow passage of the second variable throttle portion when the spool valve body is shifted a predetermined distance or more.
With this feature, since the land portion is just additionally formed on the spool valve body, the sub-passage can be cut off with a simple construction.